The present invention relates a workpiece transferring, positioning and machining system, and more particularly to a workpiece handling system for transferring a workpiece such as an automobile wheel from a stocker to a prescribed position, positioning the workpiece with a positioning device disposed in the prescribed position, and then delivering the workpiece to a machine tool with a delivery robot for desired machining operation on the workpiece, the workpiece handling system being arranged to reduce the space taken up by the machining line and lower the cost of equipment.
Various automotive parts are generally mass-produced by continuous production line processes. For example, an automobile wheel is manufactured by first producing an intermediate product by casting or forging, and conveying the product to a machine tool where it is finished on its outer and inner peripheral surfaces and formed with fastening holes for attaching the wheel to a drive axle and a valve hole.
The wheel has a plurality of hollows or recesses known as ornamental holes. The fastening holes are required to be defined accurately in a certain positional relation to the ornamental holes. Various jigs have been employed to position the wheel with respect to the machine tool.
It is known to position a wheel taken from a stocker on a jig pallet, transfer the wheel and the jig pallet to a prescribed position with a transfer device, and thereafter deliver the wheel to a machine tool with a delivery means disposed in the prescribed position. Since the wheel is positioned by the jig pallet, the wheel is retained in position against displacement during delivery, and hence can be delivered accurately to the machine tool.
For positioning the wheel on the jig pallet, it needs to be positioned by the worker or an automatic positioning device is required to position the wheel. As wheels are successively processed on the production line, the wheels that are positioned on the respective jig pallets are successively arranged on a transfer path between the stocker and the machine tool. Therefore, many jig pallets are necessary to position the respective wheels, resulting in a costly installation. After the jig pallets have been moved to the prescribed position, they have to be moved back to the stocker along a separate delivery path. Thus, where the jig pallets are employed, the cost of the jig pallets themselves and the delivery path is high, and a considerable space is needed by the delivery path.
Japanese Laid-Open Patent Publication No. 55-97886 discloses a jig device designed to eliminate the above drawbacks. The disclosed jig device includes a turntable disposed in a predetermined position on a wheel transfer path for turning a wheel and a positioning pin located in the predetermined position for engaging in the valve hole defined in the wheel. The wheel which has reached the predetermined position on the transfer path is placed on the turntable and turned thereby in one direction. The positioning pin then slidably contacts the wheel as it turns until the pin engages in the valve hole, whereupon the wheel is positioned. Thereafter, the positioned wheel is transferred to a machine tool and machined thereby as desired. The jig device of the above structure only needs to be installed on the transfer path near the machine tool, with the result that the production line can be reduced.
The above jig device is however disadvantageous in that if the wheel has irregularities on the surface for sliding contact with the positioning pin, the positioning pin interferes with the surface irregularities. The positioning pin may fail to position the wheel accurately, or may be broken by the surface irregularities. Accordingly, wheel shapes that can be positioned by the jig device are limited.